BEGINNINGS OF INTELLIGENCE 165 
a consideration of the réle of pleasure and pain as agents of 
accommodation. 
The tendency of animals to repeat acts which result in 
pleasure and to discontinue or inhibit acts which bring them 
pain is a fundamental feature of behavior on the utility of 
which it would be superfluous to comment. But why do 
animals behave in this fortunate manner, and how did they 
come to acquire the faculty of so behaving? To our ordinary ~ 
plain way of thinking it appears sufficient to say that a dog 
eats meat because he likes it, and that he runs away from the 
whip to avoid its painful incidence upon his integument. 
These acts are such natural and obvious things to do under 
the circumstances that to inquire why the animal does what 
it likes and avoids what is disagreeable may seem a sort 
of philosophic quibble which only a mind “debauched by 
learning” would think of indulging in. But a little con- 
sideration will show that we have here a real and very 
knotty problem, or rather set of problems, of the greatest 
importance to the student of genetic psychology. _ 
There are few better illustrations of the modification of 
behavior through experiences of pleasure and pain than that 
afforded by the behavior of young chicks, which has been 
so well studied by Lloyd Morgan. A young chick when 
first hatched has the instinct to peck at all sorts of objects 
of about a certain size. If an object is a little too large the 
chick may hesitate. Should it venture to peck at the object 
and derive a pleasant taste from it the hesitation in the pres- 
ence of similar objects becomes reduced and will finally 
disappear. If the chick in the course of its pecking seizes 
a caterpillar having a nauseous taste it is much less apt to 
seize a similar caterpillar a second time. The painful or 
unpleasant experience it derives in some way inhibits further 
action toward that class of objects. 
